Centrifugal
blowers come in a number of forms of which the most common is the
squirrel cage blower. The common factor is the air is moving
perpendicular to the axis of the part that is moving the air.
Typically, the air is drawn in through the side of the unit, turns at
low speed to encounter the inside of a spinning cylinder with ribs or
vanes around the wall of the cylinder which fling the air out and away
where it is captured and aimed through an outlet much smaller than the
inlet. Think of taking an open tin can, drilling a hole in the center
of the bottom to take a bolt as an axle and cutting slots up the sides,
bending the material of the slots in, then spinning it with a
drill. A variation looks like a plate with ribs running from the
center and increasing in height toward the rim, the air being thrown
off the rim. The name squirrel cage comes from the
appearance like the tread wheel small rodents use for exercise - I
suspect it is not called a hamster tread wheel because that is too
precise - or childish. Blowers can have higher output pressures, but
not a lot higher and they lose capacity rapidly with increasing
pressure. In centrifugal fan, as opposed to axial flow fan, the air is
moving perpendicularly to the fan shaft. Often called a "squirrel cage"
(due to its similarity in appearance to exercise wheels for pet
rodents), the centrifugal fan has a moving component (called an
impeller) that consists of a central shaft about which a set of blades,
or ribs, are positioned. Centrifugal fans blow air at right angles to
the intake of the fan, and spin the air outwards to the outlet (by
deflection and centrifugal force). The impeller rotates, causing air to
enter the fan near the shaft and move perpendicularly from the shaft to
the opening in the scroll-shaped fan casing. A centrifugal fan produces
more pressure for a given air volume, and is used where this is
desirable such as in leaf blowers, hair driers, air mattress inflators,
inflatable structures, and various industrial purposes. They are
typically noisier than comparable axial fans. A mixed flow fan is an
air moving device in between axial flow fan and centrifugal fan. Mixed
Flow fans are an excellent choice for return air, supply, or general
ventilation applications where low sound is critical. As compared to
similarly sized tubular centrifugals and vane axials, a mixed flow fan
will be 5-20 dB quieter! In addition, the mixed flow wheel is extremely
efficient and will cut down on operating expenses.